Ring Doorbell 2 Transformer requirements

This would apply to both the RVD and RVD2 from my understanding. I would use [t](https://shop.ring.com/products/wirewound-resistor?variant=31377537007705)he Ring wirebound resister and a transformer rated for 8-24V AV (40V maximum) at 50/60Hz. Does the 40V max mean 40 AMP max? as the doorbell supports 8-24v? Would a 16v 10va charge slower than the Ring Pro 16v 30va or a 24v 20va? What combination is the best for charging in a high use area?